1.0 Field of the Invention
The present invention relates to a ring laser gyroscope and, more particularly, to an optical mirror comprised of a stack of film pairs of alternating layers of high and low indices of refraction and used in a quantum well mirror (QWM) for a ring laser gyroscope.
2.0 Description of the Prior Art
Ring laser gyroscopes may suffer from a lock-out condition which is prevented by means of a mechanical dither spring which exists in prior art dual beam ring laser gyroscopes (RLG). The dither spring serves as a means of providing an artificial bias to the ring laser gyroscopes (RLG) at low input rates. At these low input rates and with no dither spring backscattered light from the mirrors of the RLG causes a locking of the two counter rotating beams of the RLG and hence no output. The dither spring oscillates at a set frequency rotating the RLG over a small angle. This oscillation produces an artificial input rate to the RLG keeping the RLG from locking its two beams when the externally applied input rate goes below the deadband lock-in frequency. The mechanical dither spring is made from Invar and is typically circular in design with spokes extending from a central inner ring to an outer ring. A piezo element is attached to each spoke and a voltage is applied to cause the desired oscillatory motion. The dither spring has attendant drawbacks due to its mechanical aspect.
Quantum well mirrors (QWM) may also be used to provide an optical bias so as to advantageously keep a ring laser gyroscope (RLG) out of its lock-in region. A mirror formed on dielectric materials (SiO.sub.2 and TiO.sub.2) commonly forms part of a quantum well mirror. The dielectric materials (SiO.sub.2 and TiO.sub.2) of the mirror are deposited on a polished substrate comprising, for example, quartz. The substrate requires polishing of the substrate so that its thickness is less than 1 .ANG., before the dielectric materials may be deposited. For such conditions, the yields of the fabrication process based on dielectric materials are limited because of this required polishing. It is desired that materials other than dielectric materials be utilized to provide for a mirror particularly suited to form part of a quantum well mirror (QWM) for use in a ring laser gyroscope so as to eliminate the need of a highly polished substrate.